A series of novel 2,6-bis(imino)pyridyl iron catalysts: synthesis, characterization and ethylene oligomerization

A series of novel 2,6-bis(imino)pyridyl iron complexes {2,6-(2-X-4-Y-5-ZC₆H₂NCCH₃)₂C₅H₃N}FeCl₂ (X = Cl, Y = CH₃, Z = H (2); X = Br, Y = CH₃, Z = H (3); X = F, Y = H, Z = CH₃ (4); X = Cl, Y = H, Z = CH₃ (5); X = Cl, Y = F (7)) have been synthesized and characterized with elemental analysis and IR. These iron coordinative complexes, activated with methylaluminoxane (MAO), lead to highly active ethylene oligomerization (>10⁷ g/mol Fe h) and the products are mostly linear α-olefins (>90%). The catalytic activities and product properties depend on the substituents on aryl rings and the reaction conditions. As reaction temperature increases, the catalytic activities decrease rapidly and more low-molar-mass products are produced. The product distributions are almost independent of the Al/Fe molar ratio, but the catalytic activities change in different trends when the ortho-substituents on the aryl rings are different. The other three complexes have also been synthesized for comparison to investigate the steric hindrance and electronic effect on the properties of complexes. The complex with adaptable steric hindrance and electronic properties exhibits the highest catalytic activities.